GMC 1996 Sierra Owner's Manual page 106

Electrochromic Inside Rearview Mirror
with Compass (Option)
Your vehicle may have an electrochromic inside
rearview mirror.
When on, the mirror automatically dims to the proper
level to minimize glare from lights behind you after dark.
The mirror also includes
an eight point compass
display in the upper right
corner of the mirror face.
When on, the compass
automatically calibrates
as the vehicle
is
driven.
To use the electrochromic mirror only, move the switch
at the bottom of the mirror to
the
M position. To use the
electrochromic mirror as well
a s
the compass. move the
switch to the C/M position. To turn both features off,
move the switch to the OFF position.
When the ignition is on and the mirror switch is in the
CIM position, the compass display'will show two
character boxes for approximately two seconds. If, after
two seconds, the display does not show a compass
heading (N for North, for example), there may be a
strong magnetic field interfering with the compass. Such
interference may include magnetic antenna mounts, a
magnetic note pad holder, or a similar magnetic item. If
removing these items does not correct the condition, see
your GM dealer for assistance.
When cleaning the mirror, use a paper towel or similar
material dampened with glass cleaner. Do not spray
glass cleaner directly on the mirror as that may cause
liquid cleaner to enter the mirror housing.
Compass Varia~
3
Under certain circumstances, as during a long distance
cross-country trip, it will be necessary to adjust the
compass to compensate for compass variance. Compass
variance
is
the difference between earth's magnetic
north and true geographic north. If not adjusted to
account for compass variance, your compass could give
hlse readings.
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